Set addition in boxes and the Freiman-Bilu theorem

Compressions, convex geometry and the Freiman-Bilu theorem

We note a link between combinatorial results of Bollobás and Leader concerning sumsets in the grid, the Brunn-Minkowski theorem and a result of Freiman and Bilu concerning the structure of sets of integers with small doubling. Our main result is the following. If eps > 0 and if A is a finite nonempty subset of a torsion-free abelian group with |A + A| <= K|A|, then A may be covered by exp(K^C) progressions of dimension [log_2 K + eps] and size at most |A|.

Sets in $\mathbb{Z}^k$ with doubling $2^k+δ$ are near convex progressions

For $δ>0$ sufficiently small and $A\subset \mathbb{Z}^k$ with $|A+A|\le (2^k+δ)|A|$, we show either $A$ is covered by $m_k(δ)$ parallel hyperplanes, or satisfies $|\widehat{\operatorname{co}}(A)\setminus A|\le c_kδ|A|$, where $\widehat{\operatorname{co}}(A)$ is the smallest convex progression (convex set intersected with a sublattice) containing $A$. This generalizes the Freiman-Bilu $2^k$ theorem, Freiman's $3|A|-4$ theorem, and recent sharp stability results of the present authors for sumsets in $\mathbb{R}^k$ conjectured by Figalli and Jerison.

几何提升与紧致连通阿贝尔群中Freiman的$3k-4$定理

Geometric lifting and Freiman's $3k-4$ theorem in compact connected abelian groups

本文提出几何提升方法，在紧致连通阿贝尔群中证明Freiman $3k-4$定理的类比，并建立最优投影定理，解决Christ-Iliopoulou问题，推广至流行和集与Tao卷积不等式。